全文获取类型
收费全文 | 12332篇 |
免费 | 819篇 |
国内免费 | 2388篇 |
专业分类
化学 | 13241篇 |
晶体学 | 149篇 |
力学 | 367篇 |
综合类 | 43篇 |
数学 | 68篇 |
物理学 | 1671篇 |
出版年
2024年 | 42篇 |
2023年 | 86篇 |
2022年 | 248篇 |
2021年 | 311篇 |
2020年 | 442篇 |
2019年 | 438篇 |
2018年 | 394篇 |
2017年 | 563篇 |
2016年 | 613篇 |
2015年 | 525篇 |
2014年 | 600篇 |
2013年 | 1160篇 |
2012年 | 911篇 |
2011年 | 737篇 |
2010年 | 614篇 |
2009年 | 662篇 |
2008年 | 680篇 |
2007年 | 706篇 |
2006年 | 659篇 |
2005年 | 628篇 |
2004年 | 599篇 |
2003年 | 453篇 |
2002年 | 398篇 |
2001年 | 364篇 |
2000年 | 365篇 |
1999年 | 348篇 |
1998年 | 323篇 |
1997年 | 275篇 |
1996年 | 261篇 |
1995年 | 232篇 |
1994年 | 226篇 |
1993年 | 199篇 |
1992年 | 127篇 |
1991年 | 71篇 |
1990年 | 58篇 |
1989年 | 40篇 |
1988年 | 39篇 |
1987年 | 19篇 |
1986年 | 22篇 |
1985年 | 24篇 |
1984年 | 22篇 |
1983年 | 12篇 |
1982年 | 26篇 |
1981年 | 11篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Development of new lubricating grease formulations using recycled LDPE as rheology modifier additive
The recovery of plastic waste but also its applicability in product development may be an incentive to industry, since the use of such plastics represents a cheaper source of raw material. The aim of the present paper is to study the feasibility of recycling polyolefins as additives to improve the rheological properties of lithium 12-hydroxystearate lubricating greases. The effects that both soap and recycled low-density polyethylene (LDPE) concentration exert on the rheology of lithium lubricating greases and its relationship with grease microstructure are discussed in this work. In this way, different lubricating grease formulations were manufactured by modifying the concentration of lithium 12-hydroxystearate and content of recycled LDPE, according to a RSM statistical design. These lubricating greases were rheologically characterized through small-amplitude oscillatory shear (SAOS) and viscous flow measurements. In addition to these, scanning electronic microscopy (SEM) observations and mechanical stability tests were also carried out. Recycled LDPE was found to be an effective additive to modify grease rheology, acting as filler in the soap entangled microstructure. The values of both apparent viscosity and viscoelastic functions in the linear viscoelastic region increase with soap and recycled polymer concentrations. However, the addition of recycled LDPE distort the microstructural network of these greases resulting greases with less relative elastic characteristics and poorer mechanical properties as LDPE content increases. 相似文献
82.
The synthesis and characterization of poly(4-vinyl,2′-carboxybenzophenone) ion exchange resin is described. This resin displays a remarkably high capacity for Cu2+. Control of pH permits selective adsorption and estimation of Fe3+. This ion-exchanger is quite stable to loading acid washing cycles. © 1995 John Wiley & Sons, Inc. 相似文献
83.
84.
Yi Gao Xuesong Yao Qinggeng Jiang Jianhe Liao Yongping Chen Rentong Yu 《Molecules (Basel, Switzerland)》2022,27(10)
Microgels have unique and versatile properties allowing their use in forward osmosis areas as a draw agent. In this contribution, poly(4-vinylpyridine) (P4VP) was synthesized via RAFT polymerization and then grafted to a poly(N-Isopropylacrylamide) (PNIPAAm) crosslinking network by reverse suspension polymerization. P4VP was successfully obtained by the quasiliving polymerization with the result of nuclear magnetic resonance and gel permeation chromatography characterization. The particle size and particle size distribution of the PNIPAAm-g-P4VP microgels containing 0, 5, 10, 15 and 20 wt% P4VP were measured by means of a laser particle size analyzer. It was found that all the microgels were of micrometer scale and the particle size was increased with the P4VP load. Inter/intra-molecular-specific interactions, i.e., hydrogen bond interactions were then investigated by Fourier infrared spectroscopy. In addition, the water flux measurements showed that all the PNIPAAm-g-P4VP microgels can draw water more effectively than a blank PNIPAAm microgel. For the copolymer microgel incorporating 20 wt% P4VP, the water flux was measured to be 7.48 L∙m−2∙h−1. 相似文献
85.
Olga V. Zhukova Evgenia V. Arkhipova Tatiana F. Kovaleva Daria A. Zykova Natalya A. Dubovskaya 《Molecules (Basel, Switzerland)》2022,27(14)
Cancer is a leading cause of mortality globally. Despite remarkable improvements in cancer-treatment approaches, disease recurrence and progression remain major obstacles to therapy. While chemotherapy is still a first-line treatment for a variety of cancers, the focus has shifted to the development and application of new approaches to therapy. Nevertheless, the relationship between immune response, neoplastic diseases and treatment efficiency is not fully understood. Therefore, the aim of the study was to investigate the immunopharmacological effects of methacrylic acid homopolymer in an in vivo tumor model. Materials and methods: Monomeric methacrylic acid was used to synthesize polymers. Methacrylic acid was polymerized in dioxane in the presence of 4-Cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid. To study the molecular weight characteristics of PMAA by GPC, carboxyl groups were preliminarily methylated with diazomethane. An experimental cancer model was obtained by grafting RMK1 breast cancer cells. The serum levels of IL-6, IL-10, IL-17, transforming growth factor β1 (TGF-β1), and tumor necrosis factor α (TNF-α) were measured by ELISA. Results: The effect of PMAA on the serum concentrations of several cytokines was studied upon its single administration to laboratory animals in early neoplastic process. The IL-6, IL-17 and TGF-β1 concentrations were found to change significantly and reach the level observed in intact rats. The IL-10 concentration tended to normalize. Conclusion: The positive results obtained are the basis for further studies on the effect of methacrylic-acid polymers with different molecular-weight characteristics on the neoplastic process. 相似文献
86.
Keqing Lu Kehao Li Yanpeng Zhang Changyun Miao Jingjun Xu 《Optics Communications》2010,283(23):4741-4748
We show that gray spatial optical solitons are possible in biased photorefractive polymers under steady-state conditions. We find that for a given material parameter the absolute value of a gray photorefractive polymeric soliton's phase decreases with an increase in the beam's grayness, whereas it increases with the material parameter for a given beam's grayness and that the full width half maximum (FWHM) of the gray soliton beam's intensity increases with the beam's grayness when the normalized background intensity and the material parameter are fixed and decreases with an increase in the normalized background intensity when the material parameter is fixed. On the other hand, we also show that N coupled beam evolution equations in biased photorefractive polymers can exhibit multicomponent gray solitons. These multicomponent gray solitons can be obtained provided that the N coupled beams share the same polarization, wavelength, and are incoherent with one another. The characteristics and stability properties of these multicomponent gray solitons are also discussed in detail. 相似文献
87.
王素芹 《原子与分子物理学报》2014,31(6)
在高温高压条件下利用高压合成装置合成了二维R相C60聚合物,并利用X射线衍射(XRD)和超量子干涉(SQUID)对合成的样品进行了研究.X射线衍射(XRD)数据表明,在6 Gpa压力和7000C-7250C的温度条件下合成的聚合物为纯度较高的二维R相C60聚合物,当温度升高至8000C时,富勒烯的笼状结构塌陷,样品全部变为无定形碳结构.超量子干涉(SQUID))数据表明,在富勒烯笼状结构出现破缺或共价键结构出现断裂的边界条件下制备的二维R相C60聚合物具有铁磁性,样品的磁性来源于破缺的C60分子笼和断裂的共价键. 相似文献
88.
89.
Benzothiadiazole(BT) is an electron-deficient unit with fused aromatic core, which can be used to construct conjugated polymers for application in organic solar cells(OSCs). In the past twenty years, huge numbers of conjugated polymers based on BT unit have been developed,focusing on the backbone engineering(such as by using different copolymerized building blocks), side chain engineering(such as by using linear or branch side units), using heteroatoms(such as F, O and S atoms, and CN group), etc. These modifications enable BT-polymers to exhibit distinct absorption spectra(with onset varied from 600 nm to 1000 nm), different frontier energy levels and crystallinities. As a consequence, BT-polymers have gained much attention in recent years, and can be simultaneously used as electron donor and electron acceptor in OSCs, providing the power conversion efficiencies(PCEs) over 18% and 14% in non-fullerene and all-polymer OSCs. In this article, we provide an overview of BTpolymers for OSCs, from donor to acceptor, via selecting some typical BT-polymers in different periods. We hope that the summary in this article can invoke the interest to study the BT-polymers toward high performance OSCs, especially with thick active layers that can be potentially used in large-area devices. 相似文献
90.
聚合物作为一种有机发光材料,由于在平板显示和光电子器件中的良好应用前景而受到广泛研究[1~2].近年来,一个重要进展是在聚合物中观测到了受激发射(简称Poly-mer激光)现象[3~6].Polymer激光最早是在溶液中实现的[3~4].作为一种新型... 相似文献